Non toxic activators for adhesive compositions

ABSTRACT

Non-toxic tertiary amines having very low vapor pressures and substantially insolubility in water and fats are employed as free radical catalyst activators for adhesive compositions comprising polyurethane polymers or elastomers dissolved in an addition polymerizable combination of an acrylic or methacrylic monomer, a copolymerizable monomer containing a free carboxylic acid group and a non-activated free radical polymerization catalyst.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of application Ser. No. 858,702 filed Dec. 8, 1977,now U.S. Pat. No. 4,155,950 and this application is related to U.S. Pat.No. 3,994,764 and is a continuation-in-part of copending applicationsSer. No. 705,333 filed July 14, 1976 now U.S. Pat. No. 4,080,238 andSer. No. 763,145 of Wolinski et al filed Jan. 27, 1977 now U.S. Pat. No.4,126,504 all assigned to the same assignee as the present applicationand which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

In U.S. Pat. No. 3,994,764 and the above mentioned copendingapplications there are disclosed activatable curable adhesivecompositions comprising a non-reactive polyurethane polymer or anon-reactive elastomer dissolved in a free radical additionpolymerizable methacrylic or acrylic monomer and a free radical additionpolymerizable acid monomer co-polymerizable with the methacrylic oracrylic monomer. The solution contains a non-activated free radicalpolymerization catalyst.

The patent and applications referred to show thermoplastic polyurethaneresin and elastomers such as acrylonitrilebutadiene rubbers as thenon-reactive polymers, alkyl acrylate and methacrylate esters as thepolymerizable acrylic monomers, acrylic and methacrylic acid monomers,with benzoyl peroxide as the catalyst.

As activators there are disclosed dimethylaniline, diethylaniline,N,N-dimethyl-p-toluidine. These may be admixed with an accelerator suchas a salt of copper, iron, cobalt manganese or lead, and may bedissolved in a suitable solvent.

Increased heat resistance may be imparted to the adhesive by theaddition of a relatively small percentage of a non-reactive epoxy resin.

In one method of use, the activator composition is placed on one matingsurface and the adhesive composition is placed on another matingsurface. Both surfaces are then brought together and maintained incontact relationship until the adhesive cures to a set.

Alternatively, the activator (and accelerator, if present) may beencapsulated in a microsphere which is insoluble in the adhesivecomposition. On rupturing the microsphere the adhesive will cure to aset. In one embodiment the adhesive composition is coated on one or bothmating surfaces. These are then brought into contact with sufficientpressure to rupture the microspheres. Thereafter, the surfaces are heldin contact relationship until the adhesive cures to a set. In anothermethod, the microspheres are ruptured in the adhesive solution which isthen applied to at least one of the mating surfaces and both surfacesand thereafter brought into contact. The microsphere-containing adhesiveis disclosed in detail in our copending applications Ser. No. 705,333now U.S. Pat. No. 4,080,238 and Ser. No. 763,145.

While the adhesive compositions and methods for using them are highlysatisfactory and give excellent results, care must be used in employingthe tertiary amine activators disclosed since these are irritating tothe skin and may give toxic reactions.

SUMMARY OF THE INVENTION

We have now discovered that these drawbacks may be substantiallyeliminated by employing as activators tertiary amine compounds which areessentially insoluble in water and fats, are soluble in the adhesivecomposition or solution, and which have a very low vapor pressure atordinary temperatures. These physical properties result in compoundswhich are substantially non-irritating and non-toxic although skinirritation may occur on contact in the case of some sensitiveindividuals. In addition, the low vapor pressures enable theseactivators to be coated on a surface and retain their activity for along time. Thus, a surface can be precoated with the activator andstored until it is desired to join it to another surface. At that timeone or both surfaces are coated with the adhesive solution andmaintained in contact until set is obtained.

It is the main object of this invention to have a non-toxic tertiaryamine compound as the activator for peroxy catalysts employed in a freeradical polymerizable adhesive composition.

It is a further object of this invention to employ as the tertiary amineactivators reaction products of N-methyl aniline with epoxy compounds.

It is a further object of this invention to provide tertiary amineactivators having very low vapor pressures and to coat a surface withsuch activators.

Further objects of this invention will become apparent from thespecification and claims set forth herein after.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following non-toxic activators have been prepared.

EXAMPLE 1

A one-liter reaction flask equipped with a mechanical stirrer and refluxcondenser was loaded with 2.1 moles of glycidyl methacrylate (297.5grams), two moles of N-methyl aniline (214 grams) and 100 parts permillion of hydroquinone (0.05 grams). The reaction mixture was heatedfor a total of 24 hours at 98° C. with agitation. Air was maintainedover the reaction at all times to prevent premature polymerization. Theproduct, N-phenyl-N-methyl-amino-2-hydroxy propyl methacrylate, CH₂═C(CH₃)COOCH₂ CHOHCH₂ N(CH₃)C₆ H₅, is a light green liquid with arefractive index of 1.5418, a vapor pressure of 2 mm at 162°-165° C. andof less than 0.05 mm at room temperature. The material was applied to aclean steel panel and the adhesive base of Example 1 of patentapplication Ser. No. 763,145 was applied to a second panel. The two werethen brought together and allowed to set. Setting time was 10 to 12minutes at room temperature. The bond strength in shear was 2400 lbs.per square inch and peel strength was 25 lbs. per lineal inch. Thus, anacceptable curing rate was obtained.

EXAMPLE 2

A polymer was prepared from the tertiary amine compound of the previousExample by dissolving it in toluene to form a 20% by weight solution andadding 8% by weight of benzoyl peroxide based on the monomer. Thesolution was maintained at 80° C. overnight under an atmosphere ofnitrogen. The resultant solid polymer (in toluene solution) and theadhesive base were applied to a steel panel as in the previous Example.Setting time was 10 to 12 minutes with bond peel values of 25 lbs. perlinear inch and shear values of 2500 lbs per square inch.

EXAMPLE 3

Under conditions similar to Example 2 copolymers of the tertiary aminecompound of Example 1 were made with methyl methacrylate, methylacrylate, butyl acrylate and 2-ethyl hexyl acrylate respectively, invarying ratios. It was found that the activity decreased as the amountof the amine employed decreased.

Copolymers which formed very tough films and are useful as activatorsresulted when the amine content was at least 25% by weight. With methylacrylate, 2-ethyl hexyl acrylate and butyl acrylate the films producedwere more elastomeric than the homopolymer of Example 2, or thecopolymers with methyl methacrylate.

The homopolymer and copolymers of Examples 2 and 3 are solids insolublein water and fats and have substantially no vapor pressure at ordinarytemperatures. Accordingly, they are considered to be non-toxic.

EXAMPLE 4

This example describes activators prepared from a wide variety of monoand dioxirane epoxy polymers and N-methyl aniline. The epoxy polymerswere reacted with the amine in the ratio of one mole of N-methyl anilinewith one equivalent weight each oxirane group in the respective polymer.Listed in the following table are the epoxies employed, their source,and the oxirane equivalent weight, i.e. the grams of epoxy used per 107grams of N-methyl aniline.

    __________________________________________________________________________                                Oxirane equivalent                                                            weight; grams of                                                              epoxy used with                                                               equivalent weight                                                             (107 grams) of N-                                 Class of Epoxy                                                                         Specific Polymer                                                                       Source    methylaniline                                     __________________________________________________________________________    Novolac glycidyl                                                                       DEN 431  Dow Chemical                                                                            179                                               ethers   EPN 1138 Ciba Geigy                                                                              181                                               Cycloaliphatic                                                                         ERL 4221 Union Carbide                                                                           140                                               epoxides ERL 4289 "         210                                                        CY 178   Ciba Geigy                                                                              213                                                        CY 179   Ciba Geigy                                                                              140                                               Glycidyl ethers of                                                                     DER 736  Dow Chemical                                                                            200                                               polyols  Epon 812 Shell Chemical                                                                          160                                                        Epon 828 "         195                                                        Epon 1001                                                                              "         500                                                        Epon 1007                                                                              "         2500                                                       Araldite 508                                                                           Ciba Geigy                                                                              455                                               Glycidyl ethers of                                                                     Araldite RD-1                                                                          Ciba Geigy                                                                              148                                               alcohols, polyols                                                                      Araldite RD-2                                                                          "         134                                               and phenols                                                                            Araldite DY 023                                                                        "                                                                    Epoxide 7                                                                              Proctor & Gamble                                                                        227                                               Alpha-Olefin                                                                           Vikolox 10                                                                             Viking Chemical Co                                                                      156                                               epoxides Vikolox 11-14                                                                          "         192                                               __________________________________________________________________________

The epoxy compounds were reacted with N-methyl aniline in a proceduresimilar to that in Example 1. A one liter flask was charged with a molarquantity of N-methyl aniline per mole of active oxirane, as listed inthe table. Hydroquinone on the order of 100 ppm was added to the mixturewhich was heated at 100° C. for 24 hours. In addition to the mono anddi-functional epoxy polymers shown in the table, tri-functional epoxiesmay be employed as well.

The activators produced were thick viscous resins and were tested in themanner set forth in Example 1. Setting-up time was in the range of 10 to18 minutes, peel strength of the bond averaged 20 to 25 lbs. per linearinch and the sheer strength averaged 2300 to 2500 lbs. per square inch.

The vapor pressures of the products of the secondary amines with theoxirane compounds described above are all less than 0.05 mm at roomtemperature. Many of the activator compounds described are solids, asfor example, 4,4'-methylene bis (N,N dimethylaniline) and the copolymersof Example 3. Such solid state coupled with the low vapor pressure andwater and fat insolubility lessens even further the possibility ofabsorbtion through the skin.

While about a 1:1 amino:oxirane group ratio is preferably employed withthe mono amines and the mono, di and tri functional epoxies, and withdiamines and mono epoxies, the ratio in these cases may be as low as0.25:1. However, with diamines and di and tri epoxies the 1:1 ratioresults in highly cross-linked compounds which are not soluble in theadhesive systems and hence are not suitable as activators. To obtainuseful, soluble products in the latter case, a ratio of amino oxirane ofabout 0.25:1 is employed.

Although all the examples employ N-methyl aniline, which results in theamine moiety ##STR1## other secondary amines, as illustrated in thefollowing table, may be substituted.

    ______________________________________                                        Compound          Resulting Amino Moiety                                      ______________________________________                                        N-methyl-p-toluidine                                                                             ##STR2##                                                   N-β-hydroxy ethyl aniline                                                                   ##STR3##                                                   N-ethyl aniline                                                                                  ##STR4##                                                   N-n-proply aniline                                                                               ##STR5##                                                   N-β-hydroxy ethyl-p-toluidine                                                               ##STR6##                                                   Diethanol amine   N(C.sub.2 H.sub.4 OH).sub.2                                 Dihyxyl amine     N(C.sub.6 H.sub.13).sub.2                                   p-chloro-N-methylaniline                                                                         ##STR7##                                                   N,N'-dimethyl-p-phenylene diamine                                                                ##STR8##                                                   N,N'-di-2-naphthyl-p- phenylene diamine                                                          ##STR9##                                                   N-methyl-3,5-xylidene                                                                            ##STR10##                                                  ______________________________________                                    

Most of these compounds are aromatic amines since aromatic ring groupacts to increase the electron density on the nitrogen atom which isnecessary to activate the peroxy catalyst. The two non-aromatic aminesshown, diethanol amine and dihexylamine, have the ability to likewiseactivate the peroxy catalysts, but at a slower rate.

EXAMPLE 5

The following solid, water insoluble, fat insoluble amines, having vaporpressures of less than 0.05 mm. at room temperature, were dissolved in asuitable solvent such as a chlorinated hydrocarbon and employed asactivators in an adhesive composition as described in example 1 testedon a steel panel as shown therein. The compounds have the composition##STR11## where R is H or phenyl a=0 or 1, a+b=3, and when R is phenyl,a is 1.

    ______________________________________                                                    Set Time Bond Strength                                                                              Peel Strength                               Activator   Minutes  Shear, psi   pl                                          ______________________________________                                        4,4'-methylene                                                                bis (N,N-dimethyl-                                                            aniline)    4        2700-3000    47-57                                       4,4'4"methylene                                                               tris(N,N-dimethyl-                                                            aniline)    2        2000-2500    47-57                                       p,p'-benzylidene                                                              bis(N,N-dimethyl-                                                             aniline)    2        2200-2500    50-60                                       ______________________________________                                    

Where the activator is a solid or a viscous resin solution, a suitablesolvent such as a chlorinated hydrocarbon is generally required in orderto incorporate an activator in the adhesive composition.

EXAMPLE 6

When employing the microsphere technique following the teachings ofapplications Ser. No. 705,333 and Ser. No. 763,145 the activator, suchas set forth in Examples 1-5, dissolved in a suitable solvent ifrequired, is encapsulated in a microsphere having shell or wallcomposition which is insoluble in the activator composition and in theactivatable adhesive. Chlorinated hydrocarbons solvents, which have ahigh density, are especially useful, since by their use it is possibleto adjust the density of the microspheres so that they are non-floatingin the adhesive composition.

On rupturing the microspheres, either prior or subsequent to coating onone or both mating surfaces, the adhesive becomes activated. Thereafter,on bringing the surfaces into contact, the adhesive sets and cures to astrong adhesive bond.

What is claimed:
 1. A coated article comprising a substrate havingcoated thereon an activatable curable adhesive comprising a non-reactivethermoplastic polyurethane resin or a non-reactive elastomer dissolvedin a non-acid methacrylic or acrylic monomer, and a methacrylic acrylicacid monomer, said monomers being essentially devoid of peroxy catalystactivation capability, said solution containing an effective amount of aperoxy catalyst, the said adhesive being activatable by contact with aperoxy catalyst activator; the improvement comprising having in additionin said adhesive a stable, non-toxic, peroxy catalyst activator solublein the adhesive solution, to activate the peroxy catalyst said activatorbeing selected from the group consisting of:(a) ##STR12## R=H or phenyl,a=0 or 1, a+b=3 and when R is phenyl, a is 1, (b) CH₂ ═CH(CH₃)COOCH₂CH(OH)CH₂ A, which is different from the other acrylic or methacrylicmonomers in the adhesive, wherein A is one of:

    ______________________________________                                         ##STR13##                                                                                   ##STR14##                                                       ##STR15##                                                                                   ##STR16##                                                       ##STR17##                                                                                   ##STR18##                                                       ##STR19##                                                                                   ##STR20##                                                       ##STR21##                                                                                   ##STR22##                                                                    or                                                                             ##STR23##                                                      ______________________________________                                    

(c) homopolymers of the compounds of (b) (d) a copolymer of at least 25%by weight of a compound of (b) with a member selected from the groupconsisting of methyl methacrylate, methyl acrylate, 2-ethyl hexylacrylate, or butyl acrylate, and (e) the reaction products of epoxypolymers with secondary amines selected from the group consisting ofN-methyl aniline, N-methyl-p-toluidine, N-β-hydroxy ethyl aniline,N-ethyl aniline, N-n-propyl aniline, N-β-hydroxy ethyl-p-toluidine,diethanol amine, dihexyl amine, p-chloro-N-methylaniline,N,N'-dimethyl-p-phenylene diamine, N,N'-di-2-naphthyl-p-phenylenediamine and N-methyl-3,5-xylidene, wherein from 0.25 to one aminoequivalent weight is reacted with one oxirane equivalent weight.
 2. Thearticle of claim 1 wherein the coating compound is ##STR24## where R=Hor phenyl, a=0 or 1, a+b=3 and when R is phenyl, a=1.
 3. The article ofclaim 1 wherein the coating compound isCH₂ ═CH(CH₃)COOCH₂ CH(OH)CH₂ A,wherein A is a member selected from the group consisting of:

    ______________________________________                                         ##STR25##                                                                                  ##STR26##                                                        ##STR27##                                                                                  ##STR28##                                                        ##STR29##                                                                                  ##STR30##                                                        ##STR31##                                                                                  ##STR32##                                                        ##STR33##                                                                                  ##STR34##                                                                    or                                                                             ##STR35##                                                       ______________________________________                                    


4. The article of claim 1 wherein the coating compound is an elastomericcopolymer of at least 25% by weight of N-phenyl-N-methyl-amine-2-hydroxypropyl methacrylate, and a member selected from the group of methylacrylate, 2-ethyl hexyl acrylate or butyl acrylate.
 5. The article ofclaim 1 wherein the coating compound is a co-polymer of at least 25% byweight of N-phenyl-N-methyl-amino-2-hydroxy propyl methacrylate, andmethyl methacrylate.
 6. The article of claim 1 wherein the coatingcompound is a reaction product of N-methyl aniline with an epoxy polymerformed by reacting from 0.25 mole to one mole of N-methyl aniline withone oxirane equivalent weight.